Apparatus, Method and System For Reducing Adhesive Wear On A Power Take-Off Shaft

ABSTRACT

An apparatus comprising a power take-off shaft includes an outer shaft and an inner shaft. The outer shaft includes an outer periphery and an inner periphery. The inner shaft includes an outer periphery and an inner periphery. A notch is configured around at least a portion of the outer periphery of the inner shaft, and a self-lubricating material is disposed on at least a portion of the notch.

BACKGROUND

A power take-off (PTO) shaft is a splined driveshaft that can be used todraw energy from an engine to provide power to an attachment or separatemachine. PTOs typically include an inner shaft that rotates andtranslates within an outer shaft. Certain areas of a power take-offshaft may develop adhesive wear caused by vibration and repetitivemovement between the inner shaft and outer shaft. The adhesive wear cancause binding between the inner shaft and outer shaft, and in extremecases, can prevent movement between the components. When at PTO shaftfails due to adhesive wear, the inner and outer shaft need to bereplaced resulting in maintenance cost and equipment downtime.

SUMMARY

An apparatus comprising a power take-off shaft includes an outer shaftand an inner shaft. The outer shaft includes an outer periphery and aninner periphery. The inner shaft includes an outer periphery and aninner periphery. A notch is configured around at least a portion of theouter periphery of the inner shaft, and a self-lubricating material isdisposed on at least a portion of the notch.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments disclosed herein may be better understood, and theirnumerous objects, features, and advantages made apparent to thoseskilled in the art by referencing the accompanying drawings. The use ofthe same reference symbols in different drawings indicates similar oridentical items.

FIG. 1A is a cross-sectional view of components of an embodiment of apower take-off shaft.

FIG. 1B is a side cross-sectional view of a conventional power take-offshaft.

FIG. 1C is a diagram of a side view of an embodiment of aself-lubricating sleeve that may be used on the power takeoff shaft ofFIG. 1A.

FIG. 1D is a diagram of a front view of the self-lubricating sleeve ofFIG. 1B.

FIG. 2A is a cross-sectional view of an embodiment of an inner shaftpartially engaged in an outer shaft.

FIG. 2B is a cross-sectional view of an embodiment of the inner shaft ofFIG. 2A more fully engaged in the outer shaft.

FIG. 2C is a perspective view of an embodiment of the inner shaft of thepower take off shaft of FIG. 1A.

FIG. 3 is a block diagram of an embodiment of a power take-off shaftcoupled between an engine and a gear box, including components coupledto the gear box

FIG. 4 is a diagram of an embodiment of a power take-off shaft coupledto an accessory drive gear box.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1A shows a side view of an embodiment of a powertake-off shaft 100that can be used to transmit power from an engine to other equipmentsuch as a gear box. In the embodiment shown, power take-off shaft 100includes an inner shaft 102 and outer shaft 104 that engages inner shaft102.

FIG. 1B shows a conventional power takeoff shaft including an area 106along a portion of the length of shafts 102, 104 that may be subject toadhesive wear caused by inner shaft 102′ moving within outer shaft 104.Adhesive wear is also known as scoring, galling, or seizing, and occurswhen two solid surfaces slide over one another under pressure. Surfaceprojections are plastically deformed and eventually welded together bythe high local pressure. As sliding continues, the welded bonds arebroken, producing cavities on one surface, projections on the othersurface, and frequently tiny, abrasive particles, all of whichcontribute to wear of the surfaces. The wear results in the outer shaft102′ and/or inner shaft 104 having to be removed from the equipment,discarded or repaired, and then reinstalled in the equipment.

Referring again to FIG. 1A, in some embodiments, a sleeve 108 made ofself-lubricating material can be placed in a notch 110 on the outerperiphery of inner shaft 102 to physically separate the inner shaft 102and outer shaft 104. The self-lubricating sleeve 108 reduces adhesivewear by providing a self-lubricated surface that supports contactbetween the inner and outer shafts 102, 104, thereby preventing theinner shaft 102 and outer shaft 104 from coming into direct contactduring operation. FIG. 1A shows sleeve 108 separate from inner shaft 102and including a slot 112 that allows the ends of sleeve 108 to beseparated to create space to allow sleeve 108 to be disposed in notch110. Sleeve 108 can be made of resilient material that allows sleeve 108to be easily removed and replaced while shafts 102, 104 are installed inthe equipment, thereby reducing maintenance costs and equipmentdowntime.

In the embodiment shown, inner shaft 102 can further include o-ring 114disposed in groove 116 to seal lubricating oil between another portionof the lengths of inner shaft 102 and outer shaft 104. Inner shaft 102and outer shaft 104 can include one or more openings 118, 120 to allowlubricating oil to flow between the shafts 102, 104.

A spline gear 122 can be configured around the periphery of one endinner shaft 102 while another end of inner shaft 102 can include aflange 124 for mounting shaft 102 on equipment. The internal peripheryof one end of outer shaft 104 can include a spline gear 126 that mateswith the spline gear 122 of inner shaft 102. Spline gears 122, 126rotate to transfer power from equipment attached to the flange 124 ofinner shaft 122 to equipment attached to outer shaft 104.

In an embodiment, gears 122, 126 are configured without an angle so thatthe gear teeth are parallel to the axis of shafts 102, 104. In thisconfiguration shaft 102 rotates and transmits power to outer shaft 104.The linear configuration of gears 122, 126 allows outer shaft 104 tomove axially over shaft 102 with minimal resistance. Shaft 102 and outershaft 104 typically have an internal periphery and an externalperiphery. The distance between the internal and external periphery ofeach shaft 102, 104 is the shaft thickness; although this thickness mayvary over the length of the shaft. The thickness of each shaft issufficient to transmit the maximum force to be transmitted by system100.

FIGS. 1C and 1D depict respective end and side views of sleeve 108including slot 112. Slot 112 allows sleeve 108 to be opened and closedto be removed and replaced on shaft 102 without disconnecting shaft 102from the equipment. Slot 112 can be made at an angle so that regardlessof the load direction, the shaft 102 will always bear against a solidsection of sleeve 108. The spacing of slot 112 is typically kept to aminimum and sized to prevent binding due to thermal expansion. In someapplications, slot 112 is 0.020-0.040 inches, but other suitable gapsizes can be used. Slot 112 can be oriented at an angle typicallyranging from from 10 to 45 degrees. For example, in some embodiments,slot 112 is oriented at a 15 degree angle.

In some embodiments, the thickness of sleeve 108 is designed to protrudea predetermined amount, for example 0.04″ or other suitable distance,above the adjacent periphery of shaft 102. The exact thickness of sleeve108 may be chosen to be large enough to separate shaft 102 from outershaft 104, but small enough not to cause excess interference.Manufacturing sleeve 108 from a non-metallic material can help reduceheat buildup, vibration and corrosion between sleeve 108 and shaft 102and also between sleeve 108 and outer shaft 104.

Sleeve 108 may be made from acetal, fluoroplymer, nylon, or othersuitable material. RULON® is a specially compounded fluoropolymer, whichmay be particularly suitable for use as sleeve 108 due to its lowcoefficient of friction and an excellent abrasion resistance tocorrosion. Rulon requires no lubrication and may perform well undersevere temperature (−400° to +550° F.) and corrosive conditions. Inparticular, Rulon has increased wear resistance, lower deformation underload, greater stiffness and higher compressive strength than nylon.Rulon is commercially available from Saint Gobain Performance Plasticsin Aurora, Ohio, which is a division of Saint Gobain Company ofCourbevoie France.

FIG. 2A is a cross-sectional view of an embodiment of inner shaft 102partially engaged in outer shaft 104. FIG. 2B is a cross-sectional viewof the inner shaft 102 of FIG. 2A more fully engaged in the outer shaft104. FIGS. 2A and 2B also include a series of arrows depicting the flowdirection of lubricating oil from an external pump to the internalperiphery of shaft 102. From the internal periphery of shaft 102 thelube oil flows to the outer periphery of shaft 102 through lube oilreturn holes 118. From the outer periphery of shaft 102 the lube oil mayreturn to the lube oil system (not shown) through lube oil return holes120 in outer shaft 104. The number and diameter of lube oil return holes118 and 120 are designed to maintain a predetermined flow and pressureat various parts of the system, including the interface of spline 122and spline 126. If the number and/or diameter of lube oil return holes118 and/or 120 is too small, the flow will be restricted andinsufficient oil will be provide to lubricate splines 122, 126. If thenumber and diameter of lube oil return holes 118 and 120 are too large,then the flow to splines 122, 126 may be sufficient, but the flow toother parts of the system may be insufficient.

FIG. 2C is a side perspective view of an embodiment of the inner shaft102 showing splines 122 in more detail. Splines 122 are configured toallow linear movement between inner shaft 102 and outer shaft 104. Thus,PTO 100 may function as an expansion joint between equipment mounted toshafts 102, 104.

Referring to FIG. 3, a block diagram of an embodiment of system 300 isshown including inner shaft 102 and outer shaft 104 coupled betweenengine 302 and gear box 304. In the embodiment shown, shaft 102 can becoupled to engine 302 by flange 124. Outer shaft 104 is configured ingear box 304 to drive various components such as starter 306, hydraulicpump 308, alternating current (“A/C”) generator 310, and direct current(“D/C”) generator 312. When necessary, starter 306 may provide powerthrough gear box 304 to start engine 302. Note that other suitableequipment can be coupled to gear box 304.

Referring to FIGS. 1 and 4, a diagram of an embodiment of system 400 isshown with PTO 100 installed in Airframe Mounted Accessory Drive (AMAD)gear box 402. Gear box 402 is configured to drive D/C generator 404, A/Cgenerator 406, starter 408 and hydraulic pump 410. Flange 124 may becoupled to a flange on the engine (not shown). PTO 100 often experiencesadhesive wear that prevents shaft axial movement, increasing stresses inPTO 100. The wear results in the inner shaft 102 having to be discardedand replaced during phase inspections. The outer shaft 104 also wearsbeyond limits resulting in the gear box 402 being removed from theaircraft and returned to the vendor prior to its normal life cycle. Thepremature wear poses a significant cost and maintenance issue with someaircraft programs. Using sleeve 108 helps prevent the gear box 402 fromhaving to be removed from the aircraft and returned to the vendor forrepair prior to completing its full life cycle. Sleeve 108 also helpsprevent having to discard the inner shaft 102 at each inspection. Notethat existing shafts 102 can be retrofitted with notch 110 therebyextending the life of PTOs 100 currently in service.

While the present disclosure describes various embodiments, theseembodiments are to be understood as illustrative and do not limit theclaim scope. Many variations, modifications, additions and improvementsof the described embodiments are possible. For example, those havingordinary skill in the art will readily implement the processes necessaryto provide the structures and methods disclosed herein. Variations andmodifications of the embodiments disclosed herein may also be made whileremaining within the scope of the following claims. The functionalityand combinations of functionality of the individual modules can be anyappropriate functionality. Additionally, limitations set forth inpublications incorporated by reference herein are not intended to limitthe scope of the claims. In the claims, unless otherwise indicated thearticle “a” is to refer to “one or more than one”.

1. An apparatus comprising: a power take-off shaft including an outershaft and an inner shaft, the outer shaft including an outer peripheryand an inner periphery, the inner shaft also including an outerperiphery and an inner periphery; a notch around at least a portion ofthe outer periphery of the inner shaft; and a self-lubricating materialdisposed on at least a portion of the notch.
 2. The apparatus of claim1, further comprising: a groove around at least a portion of the outerperiphery of the inner shaft; an o-ring, the inside diameter of theo-ring in the groove around at least a portion of the outer periphery ofthe inner shaft.
 3. The apparatus of claim 1, further comprising theself-lubricating material protrudes above the notch.
 4. The apparatus ofclaim 1, further comprising the self-lubricating material is configuredas a hollow cylindrical sleeve including a slot to allow the sleeve tobe installed and removed on the inner shaft.
 5. The apparatus of claim1, further comprising the self-lubricating material configured as acylinder including a slot sized to allow the sleeve to expand duringoperation without overlap
 6. The apparatus of claim 1, furthercomprising the self-lubricating material configured as a cylinderincluding a slot in the periphery of the cylinder, the slot being at anangle of more than fifteen (15) degrees but less than seventy (70)degrees with respect to an axis of the cylinder.
 7. The apparatus ofclaim 1, the inner shaft further comprising: a spline; a first set oflube oil return holes extending from the inner periphery of the innershaft to the outer periphery of the inner shaft; and a second set oflube oil return holes extending from the inner periphery of the outershaft to the outer periphery of the outer shaft.
 8. The apparatus ofclaim 1, the inner shaft further comprising an o-ring, the o-ringincluding an inside periphery and an outside periphery, the insideperiphery of the o-ring adjacent to the inner shaft, the outsideperiphery of the o-ring adjacent to the outer shaft.
 9. The apparatus ofclaim 1, further comprising: an engine coupled to the inner shaft. 10.The apparatus of claim 1, further comprising: a gear box coupled to theouter shaft.
 11. The apparatus of claim 1, further comprising theself-lubricating material chosen from one of the following group ofmaterials: fluoropolymer, nylon, polytetraflouroethylene (“PTFE”), and anon-metallic material.
 12. The apparatus of claim 1, further comprising:the inner shaft including a spline; a lubricating pump; and an o-ringconfigured to seal lubricating oil between a portion of the inner andouter, the lubricating oil is circulated by the lubricating pump throughlube oil return holes in the inner and outer shafts.
 13. The apparatusof claim 1, further comprising: a gear box coupled to the power takeoffshaft and configured to drive at least one of the group consisting of: ahydraulic pump; a direct current generator; an alternating currentgenerator; and a starter motor.
 14. A power take-off shaft comprising: afirst shaft means including an outer periphery, the outer peripheryincluding a notch; a second shaft means configured to slide over atleast a portion of the first shaft; and, a self-lubricating sleevemeans, the self-lubricating sleeve means disposed on the notch of thefirst shaft.
 15. The apparatus of claim 12, further comprising theself-lubricating sleeve means including: a proximate side and a distalside; and a slot extending from the proximate side of the sleeve meansto the distal side of the sleeve means.
 16. A method comprising:uncoupling a first shaft from an engine, the first shaft being acomponent of a power takeoff shaft; and installing a self-lubricatingsleeve in a notch around the periphery of the first shaft withoutuncoupling a second shaft that is a component of a power take-off shaftfrom a gear box.
 17. The method of claim 16, further comprising:removing the self-lubricating sleeve from the first shaft withoutuncoupling the power take-off shaft from the gear box.
 18. The method ofclaim 16, further comprising: the self-lubricating sleeve ismanufactured from of one of the group of materials consisting of:fluoropolymer, nylon, polytetraflouroethylene (“PTFE”), acetal, and anon-metallic material.
 19. A system, comprising: a gear box coupled toat least one of the group consisting of: a starter; a direct current(“DC”) generator; an alternating current (“A/C”) generator, a hydraulicpump, and a starter motor; a power take-off shaft coupled to the gearbox, the power take-off shaft including a notch in an outer periphery; aself-lubricating sleeve disposed on the notch; an engine; and a secondshaft coupled to the engine, the second shaft configured to slide overat least a portion of the power take-off shaft.
 20. The system of claim19, further comprising: the self-lubricating sleeve is manufactured fromof one of the following group of materials consisting of: fluoropolymer,polytetraflouroethylene, acetal, or nylon, and a non-metallic material.21. The system of claim 19, further comprising the self -lubricatingsleeve is a hollow cylinder, the cylinder including a proximate side anda distal side, and a slot from the proximate side of the sleeve to thedistal side of the sleeve.
 22. The system of claim 19, furthercomprising: the thickness of the self-lubricating sleeve is greater thanthe depth of the notch.
 23. The system of claim 19, further comprising:a lube oil pump, the discharge of the lube oil pump directed into theinner periphery of the power take-off shaft; the power take-off shaftincluding an o-ring and oil return slots; and the first shaft includinglube oil return slots, the lube oil return slots through the outerperiphery of the power take-off shaft to the inner periphery of thepower take-off shaft.